The present invention is an improvement on apparatuses and methods for removing the unhardened portion of a coating. This invention, in its preferred embodiment, is used to clean photopolymer printing plates. However, it would be clear to anyone skilled in the art from the discussion of the invention in the context of a photopolymer printing plate that it will have wide utility in a broad range of applications when portions of coatings are removed from a substrate.
Modern printing now commonly utilizes printing plates having photographically produced relief images. These photoplates are usually made of a laminated structure. This structure usually consists of a thin coating of a photosensitive composition bonded to a metal or plastic substrate. The desired image is usually obtained by placing the plate in a vacuum frame with the negative firmly affixed against the plate. The plate is then exposed to electromagnetic radiation, usually ultraviolet light. This exposure causes certain areas of the photosensitive composition to harden while others remain soft when exposed to the proper solvents. The plate is then scrubbed to remove the unhardened photosensitive composition, thereby producing the desired relief image.
This invention is an improvement on the present methods and apparatuses used to scrub the plate to remove the unhardened photosensitive composition. The machines which are presently used to perform the washout step, use large brushes or multiples of smaller flat brushes. These brushes are usually driven in an orbital or oscillating horizontal manner which simulates hand or manual scrubbing. Because of the complicated orbital and oscillating manner these brushes move, these machines are very large and very expensive. In fact, due to the size and cost of these machines, many plates are still washed by hand. Hand washing is, however, very difficult and time consuming and cannot be done uniformly or efficiently.
Thus, the object of this invention is to produce a machine that washes the plates uniformly and efficiently as well as being inexpensive and compact. The main feature of the invention to achieve this objective is to place the plates on the walls of a cylindrical tank filled with solvent. A carrousel with cylindrical brush is placed in the tank. An electric motor drives the carrousel and causes the brushes to rub against the plates. The advantages of my invention over the previous art is that it is compact and less expensive to make and use. Most of the machines designed to wash out plates of 25 inches.times.18 inches in the previous art weight between 400 lbs. and 2000 lbs. and take up between 9 and 30 square feet of floor space; whereas my invention to wash out the same size plate weighs 45 pounds and takes up approximately one square foot of floor space.